Electromagnetic actuator

ABSTRACT

An electromagnetic actuator includes an external movable plate formed integrally with a semiconductor substrate. A first torsion bar movably supports the movable plate with respect to the semiconductor substrate. An internal movable plate is disposed inside the external movable plate. A second torsion bar rotatably supports the internal movable plate relative to the external movable plate, and is positioned at a right angle relative to the first torsion bar; and further includes a single turn first driving coil extending around the external movable plate; a single turn second driving coil extending around the internal movable plate, and which is connected in series with the first driving coil; magnetic field generating means for applying a magnetic field to the first and second driving coils; and an optical element having an optical axis and located on the internal movable plate. A current is caused to flow through the first and second driving coils to produce a force corresponding to each coil and to each plate, the external and internal movable plates displacing in response to the corresponding coil forces applied thereto and thus vary the direction of displacement of said optical axis. In one embodiment, the single turn first and second driving coils are closed-looped. A method of manufacturing the electromagnetic actuator includes forming an aluminum layer on the semiconductor substrate by aluminum deposition; and forming the driving coils from the aluminum layer through photolithography and aluminum etching. Other embodiments are disclosed.

This application is a division of application Ser. No. 08/793,386 filedApr. 25, 1997, now U.S. Pat. No. 6,232,861.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic actuator based onthe operation principle of galvanometer operated mirror utilizing theprocess for manufacturing semiconductor devices, such as transistors orintegrated circuits.

2. Brief Description of the Related Art

Examples of electromagnetic actuators of such a type are disclosed inJapanese laid-open publication Nos. 5-320524, 6-9824 6-310657 and6-327569.

Disclosed in Japanese laid-open publication Nos. 5-320524 is afundamental model of an electromagnetic actuator of this type,comprising a semiconductor substrate, on which a movable plate and atorsion bar are integrally mounted, wherein the torsion bar swingablysupports the movable plate with respect to the substrate, a driving coilis formed around the movable plate, a galvanometer operated mirrormounted to the movable plate, and means for generating a magnetic fieldfor applying a magnetic field for the driving coil; and the movableplate is driven by the galvanometer operated mirror by flowing a currentthrough the driving coil.

Laid-open publication No. 6-9824 discloses substantially the fundamentalmodel as described above, but modified in that a detection coil forpositional detection of the movable plate is connected to the drivingcoil.

Laid-open publication No. 6-310657 discloses an optical detector of thetype in which the direction of the optical axis is variable, wherein themirror in the galvanometer operated mirror disclosed in No. 5-320524 orNo. 6-9824 is replaced by a photo-dedector element.

Finally, Laid-open publication No. 6-327369 discloses an electromagnetic actuator of the type, such as galvanometer operated mirror oroptical axis variable type, in which a torsion bar is made ofelectro-conductive to form an electric connection, so as to preventdisconnection of the wir-ing pattern around the torsion bar caused bythe repetition of torsional action of the torsion bar.

The electromagnetic actuator disclosed in Laid-open publication No.6-310657 is described below as to the embodiment thereof.

Related Art 1

With reference to enlarged views of FIGS. 32 and 33, as the related art1, the arrangement of “an optical detector of the type in which thedirection of the optical axis is variable” is described. The examples ofthe related arts 1 to 3 hereinafter are all of the type which ope-ratesby the same principle of the galvanometer. Also, the drawings includingFIGS. 34 to 39 are all enlarged views.

In FIGS. 32 and 33, the optical detector 1 of the type in which thedirection of the optical axis is variable is composed of a three-layeredstructure, including a silicone base 2 as a semiconductor subst-rate,and a pair of borosilicate glass bases 3 and 4 bonded on the upper andlower surfaces of the silicone base.

Here, there is the Joule's loss due to the resistance component in thecoil, and sometimes the driving ability is limited due to generatedheat, and, therefore, the flat coil 7 is formed by electroforming,comprising the steps of: sputtering a thin nickel layer on a substrate,forming thereon a copper layer by Cu electrolytic plating, and removingpart of Cu and Ni layer leaving the coil pattern to form the flat coil,featured in forming the thin layer coil with low resistance and highdensity, providing the micromagnetic device with miniaturized andthinned profile.

On the upper central area of the coil, a pn photodiode 8 is formed in aknown process, and a pair of electrode terminals 9, 9 connect to theflat coil 7 via the portion of torsion bar 6, where the terminals 9, 9are formed simultaneously with forming of the flat coil 7.

On both sides, referring to FIG. 32, of substrates 3 and 4, eachpair-formed annular permanent magnets 10A, 10B and 11A, 11B apply amagnetic field to the flat coil, on the region parallel with the torsionbar axis. Three pairs of magnets 10A, 10B, each pair therein beingvertically arranged, are located such that the polarity is uniform,e.g., all N-poles locate lower sides, and S-poles upper sides as in FIG.33. Similarly, the other three pairs 11A, 11B are located so as to havethe polarity opposite to the above-mentioned pairs 10A and 10B.

Also, on the lower side of the glass base 4, a pair of coils arepatterned and provided, which are connected to the paired terminals 13and 14 (Schematically depicted by one dotted line in FIG. 32, butactually a plurality of turns). The detection coils 12A, 12B are locatedsymmetrically relative to torsion bar 6, to detect the displacementangle of movable plate 5, and are located so that the mutual inductancebetween the flat coil 7 and detection coils 12A, 12B varies so as toincrease when one of these approaches the other, and decrease when theother is away from the other. For example, by detecting the change ofthe voltage signal produced due to the mutual inductance, thedisplacement angle of movable plate 5 can be detected.

In operation, when a current is flowed across one terminal 9 and theother terminal 9 as + and − electrodes, respectively, a magnetic fieldis formed so as to cross the flat coil 7 as the arrows B in FIG. 34shows. When a current flows via the coil 7, a force F is applied on flatcoil 7, or, in other words, across the ends of movable plate 5, in thedirection according to the Flemming's left-hand law, and such a force isobtained by the Lorentz' law.

The force F is obtained by the following formula (1), when i is currentdensity flowing across the coil 7, and B is magnetic flux formed by theupper and lower magnets:

F=i*B  (1)

Actually, depending on the turn number n of coil 7, and the coil lengthw along which the force F is applied, the force F is again:

F=nw(i*B)  (2)

On the other hand, by rotation of movable plate 5, the torsion bar 6 istilted, and the relation between the opposed spring force F′ and thedisplacement angle φ of movable plate 5 is as follows:

φ=(Mx/GIp)=(F′L/8.5*109 r4)*11  (3)

Where Mx: torsional moment, G: lateral elastic coefficient, Ip: polarsectional secondary moment. L, 11 and r are, respectively, the distancefrom the central axis to the force point, the length of the torsion bar,and the radius of torsion bar as shown in FIG. 34 .

As the movable plate 5 rotates until where the forces F and F′ reach totheir balanced state, the displacement angle varies in proportional withthe current “I”.

By controlling the current flowing via the coil 7, the object beingmonitored can be traced in a one-dimensional manner about an axis.

The induced voltage generated in detection coils 12A and 12B variesaccording to the displacement of optical detector element 8: thereby thedetection of such voltage allows to detect the optical axis displacementangle φ of the detector element 8.

Also, by the arrangement in FIG. 35 as including a differentialamplifier circuit, the optical axis displacement angle φ can becontrolled in a precise manner.

In the above-describe Related art, the movable assembly can be typicallysmall-sized and light-weight. No compensation for the dispersion ofcomponent parts is required.

Related Art 2

An “optical axis direction variable-type photo-detector” is shown inFIG. 36, compared with the Related art 1, a two-axis photo-detector isprovided, having a pair of torsion bars perpendicular with each other.

In FIG. 36, the optical axis direction variable-type photo-detector 21,having the three layered construction, includes a silicon substrate 2and a pair of upper and lower glass substrates 3, 4 bonded together. Oneach center of substrates 3 and 4, a pair of rectilinear recesses 3A, 3Bare formed. The glass substrates 3, 4 each is bonded on the siliconsubstrate 2 in the manner that the upper glass substrate 3 is placed onthe Si substrate 2 with the recess 3A on the lower side to be bondedthereon, while the lower glass substrate 4 is placed with the recess 4Aon the upper side to be bonded on the Si substrate 2. As a result, aspace is provided, in which the movable plate 5 having a detectionelement 8 thereon is allowed to rock therein.

In operation, a current flowed across the coil 7A causes the ext-ernalmovable plate 5A to rotate around the first torsion bars 6A, 6Aaccording to the current direction, wherein the internal movable plate5B also rotates integrally with the external movable plate 5A, and thephotodiode 8 operates in the same manner as the case of the Related art1.

The object to be monitored can be traced in a two-dimensional manner.

Related Art 3

As shown in FIGS. 37, 38 and 39, an optical axis direction variable-typephoto-detector is provided. Different from the Related art 2, either ofglass substrates 3, 4 is formed in a flat shape having no recesses 3A,4A. Instead, a rectilinear opening 3 a is formed in the movable plate 3for allowing the detection light to directly enter the photodiode 8.

Variations

Other variations are possible for the optical detector element insteadof a photodiode, such as a line sensor or an area sensor, eachcomprising a plurality of photodiodes. Also, phototransistors,photo-conductors, or CCD may be employed. As necessary, microlens forconverging the incident light is provided in front of the opticaldetector element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment 1 of the invention;

FIG. 2 is an illustrative view (No.1) of the production process of theembodiment 1;

FIG. 3 is the additional illustrative view (No.2) of the productionprocess of the embodiment 1;

FIG. 4 is the additional illustrative view (No.3) of the productionprocess of the embodiment 1;

FIG. 5(a) is a schematic view describing the driving process of theembodiment 1;

FIG. 5(b) is a diagram useful for explaining the operation of theembodiment of FIG. 5(a);

FIG. 6 is an illustrative view (No.1) of the production process of anembodiment 2;

FIG. 7 is another illustrative view of (No.2) of the production processof the embodiment 2;

FIGS. 8(a) and (b) each is an end view illustrating wiring formed on thetorsion bars;

FIG. 9 is a perspective view of an embodiment 3;

FIG. 10 is a perspective view showing the magnet arrangement;

FIGS. 11(a), 11(b) and 11(c) are fragmentary views of a torsion bar;

FIG. 12 is a fragmentary view of a cantilever;

FIG. 13 is another view of a torsion bar;

FIG. 14 is an illustrative view No.1 of the production process of theembodiment 3;

FIG. 15 is an illustrative view No.2 of the production process ofembodiment 3;

FIG. 16 is an illustrative view No.1 of the production process of anembodiment 4 ;

FIG. 17 is an illustrative view No.2 of the production process ofembodiment 4 ;

FIG. 18 is an illustrative view No.1 of the production process of anembodiment 5;

FIG. 19 is an illustrative view No.2 of the production process ofembodiment 5;

FIG. 20 is an illustrative view No.1 of the production process of anembodiment 6;

FIG. 21 is an illustrative view No.2 of the production process ofembodiment 6;

FIG. 22 is an illustrative view No.3 of the production process followingto FIG. 20;

FIG. 23 is a perspective view of an embodiment 7;

FIG. 24 is an illustrative view No.1 of the production process of a tipof the embodiment 7;

FIG. 25 is an illustrative view No.2 of the production process ofembodiment 7;

FIG. 26 is an illustrative view of the production process of a supportsubstrate of the embodiment 7;

FIG. 27 is an illustrative view of the assembly process of embodiment 7;

FIG. 28(a) is a schematic view describing the driving process of theembodiment 7;

FIG. 28(b) is a diagram useful in explaining the operation of thecircuit device of FIG. 28(a);

FIGS. 29(a) and 29(b) are diagrammatic views illustrating the resonanceproperty;

FIG. 30 is a schematic view of embodiment 8;

FIG. 31(a) is a schematic view describing the driving process of anembodiment 9;

FIG. 31(b) is a diagram useful for explaining the operation of thecirucit device of FIG. 31(a).

FIG. 32 is a plan view of the device of Related Art 1;

FIG. 33 is a sectional view of FIG. 32;

FIG. 34 is a perspective view of the device of the Related Art 1;

FIG. 35 is a principle diagram for angle detection in the Related Art 1;

FIG. 36 is a perspective exploded view of the Related Art 2;

FIG. 37 is a plan view of the Related Art 3;

FIG. 38 is a sectional view taken along B—B of FIG. 37; and

FIG. 39 is a sectional view taken along C—C of FIG. 37.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

FIG. 1 shows a summary view of an embodiment of an electromagneticactuator 100, in which the direction of the optical axis of an opticalunit (including a mirror, light receiving element, light emittingelement, etc) 104 is allowed to swing within a two-dimensional surface,wherein a first and a second driving coils 102 and 103, respectively,are each a one-turn coil of thin film, and connected in series to eachother.

The embodiment differs from the Related Art 2 in construction of thedriving coil, in arrangement of the permanent magnet, and in the methodof actuating the electromagnetic actuator. But the modified arrangementof the magnet does not cause a variation of the function as anelectromagnetic actuator, and rather provides advantages, by utilizing acomponent of magnetic flux perpendicular to the driving coil, to reducethe number of permanent magnets, to simplify the construction and reducethe production cost.

The process of producing the electromagnetic actuator is described inreference to FIGS. 2 to 4, wherein the thickness is exaggerated relativeto the horizontal dimension for clarity, as is the same in FIGS. 6 and 7described hereinafter.

The right side figures in both of FIGS. 2 and 3 are plan views, and leftside figures are sections taken along lines A-A′ of the right sideFigures. In step (a), oxide layers 201 and 202 are formed on the upperand lower surface of a silicone substrate 200. In step (b), the oxidelayer 202 is partial-ly removed by photolithography and oxide-layeretching, but leaving a peripheral area 203, an external movable area 204and an internal mova-ble area 205. In step (c), a thin oxide layer 206is formed on the areas where the oxide layer has been removed in step(b). In step (d), the oxide layer 206 is partially removed byphotolithography and oxide-layer etching, but leaving the areas of afirst torsion bar 207 and a second torsion bar 209. In step (e), theareas removed in step (d) is processed by anisotropic etching. In step(f), the oxide layer still remaining is removed. In step (g), byanisotropic etching, a first torsion bar 207, external movable plate208, second torsion bar 209 and an internal movable plate 210 is formed.

In step (h), aluminum layer 211 is formed on the oxide layer 201 of theupper surface of silicon base 200 by aluminum evaporation. In step (i),the aluminum layer 211 is partially removed by photolithography andaluminum etching to simultaneously form a terminal 212, a wiring 213 onthe first torsion bar, a first driving coil 102, a wiring 214 on thesecond torsion bar, a second driving coil 103, and a mirror 215 as anoptical element.

As can be seen, the first and second driving coils are connected inseries, and connected to terminal 212.

In step (j), an organic protective layer is formed by photoli-thographyso as to surround the first and second driving coils 102 and 103. Instep (k), the oxide layers 217, 218 and 202 are removed by oxide layeretching, including one 217 intermediate between the fringe area 203 andexternal movable plate 208, another oxide layer 218 between the externaland internal movable plates 208 and 210, and the remaining oxide layer202, to form a chip 101.

In step (1), the chip 101 above is placed on and bonded to a separatelyprepared silicone base 220 having a recessed region 219 in the middlethereof, and in step (m), a pair of permanent magnets 105 and 106 aremounted in diagonal relationship to complete an electromagnetic actuator100.

To operate the electromagnetic actuator 100, in which the first andsecond driving coils are connected in series to each other, and bothcoils are driven by the same current flow, different from the RelatedArt 2. Therefore in the invention, utilizing the difference between theresonant frequencies of the external movable plate 208 driven by thefirst driving coil 102 and internal movable plate 210 driven by thesecond driving coil 103, the external and internal movable plates areseparately driven so as to allow the optical element 104 on the internalplate 210 to swing in two-dimensional directions, i.e., about twoorthogonal axes.

Suppose that the resonant frequency of the external and internal movableplates are, respectively, 400 and 1600 Hz. As shown in FIG. 5(a), thevariable sinusoidal altenating source 51 having 400 Hz(f1) and an outputvoltage el, and the variable sinusoidal altenating source 52 having 1600Hz(f2) and an output voltage e2, are connected in series and furtherconnected to the terminal 212 of the electromagnetic actuator 100.

As a result, the external movable plate 208 is activated by the voltagegenerated from the a.c. source 51 and is resonated in oscillation at 400Hz relative to X-axis, while the internal movable plate 210 is alsoactivated by the voltage generated from the a.c. source 52 and isresonated in oscillation at 1600 Hz relative to Y-axis. Thus, as shownin FIG. 5(b), the direction of the optical axis of the optical element104 oscillates in the two-dimensional manner as a Lissajous figuretraces. When the ratio between the resonant frequencies of external andinternal movable plates is set to be an integer, the Lissajous figureturns to move with the time, and thus fine scanning becomes possible.The swing in the X-direction varies in accordance with changing thevoltage of the a.c. source 51, while the swing in the Y-direction variesin accordance with changing the voltage of the a.c. source 52. Themechanical Q of the movable plate of the electromagnetic actuator ofthis type at a resonant state is high, and the amplitude issubstantially decreased, when the source frequency varies even byseveral Hz. Accordingly, neither the internal movable plate 205 would beactivated to oscillate by a.c. source 51, nor the external movable plate208 would be activated to oscillate by ac source 52. Also, because ofutilizing resonance, and because it is impossible to detect thedisplacement angle of the movable plate by means of a detecting coil tofeedback control the dis-placement angle, a coil for detection is notneeded.

The arrangement shown in FIG. 5(a) is an example of actuation with avoltage source having a small internal impedance, while, when actuatedby a source having a large internal impedance, both voltage sources arenormally connected to the terminal 212.

As discussed above, in the present embodiment, since the coils areconnected in series with each one turn, the number of terminals, ofwiring on each torsion bar, or of turns of each driving coil is reduced,thereby the construction being largely simplified. Since the coils,terminals, the wiring of torsion bars, and the mirror, are all formed byphotolithography and aluminum etching, the number of masks needed forthe process is largely reduced to simplify the production processes withlowered costs.

As the wiring on driving coils and torsion bars, formed of depositedaluminum layer, are thin enough and soft compared with the copper layerprepared by electroforming coil method as that in the Related Art 2, thecharacteristics are stably maintained for a long period of life.

Embodiment 2

In the present embodiment, there is no need of providing the seconddriving coil so as to have a one-turned closed circuit, or recesses asis in embodiment 1, or spacers as is in Related Art No.3.

The process of manufacturing the embodiment is described referring toFIGS. 6 and 7, comprising the steps of:

(a) forming oxide layers 301 and 302 on both surfaces of siliconsubstrate 300;

(b) partially removing the oxide layer 302 by photolithography and oxidelayer etching, leaving the peripheral area 303;

(c) forming a thin oxide layer 304 on the area of which the initialoxide layer has been removed;

(d) removing the oxide layer 304 by the same process as above, butleaving regions including the first torsion bar 305, external movableplate 306, second torsion bar 307 and internal movable plate 308;

(e) providing anisotropic etching on the area removed at the foregoingstep (d);

(f) removing the still remaining oxide layer 304 by oxide layer etching;and

(g) further providing anisotropic etching on the lower surface.

In step (h), aluminum layer 309 is formed on the oxide layer 301 byaluminum deposition.

In step (i), the aluminum layer 309 is partially removed byphotolithography and aluminum etching to simultaneously form a firstdriving coil 310 formed of a one-turned loop, a second driving coil 311also formed of a one-turned loop, and a mirror 312 as an opticalelement.

In step (j), an organic protective layer is formed by photolithographyso as to surround the first and second driving coils 310 and 311.

In step (k), the unneeded region of the oxide layer 301 is removed byoxide layer etching to form a chip 320.

In step (l), the tip 320 above is placed on and bonded to a separatelyprepared Pyrex glass base 321 by anode bonding.

The herein referred anode bonding is a technique such that, with thesilicon and glass bases facing together with each of smooth surfaces,after heated up to 400° C. a 100 V negative voltage is applied on theglass side to bond with each other, wherein an ionic deviation in theglass base is caused, and are bonded together, by way of a staticattractive force produced between the silicon and glass bases andchemical bonding between the boundary surface.

Since the first driving coil 310 and second driving coil 311 are bothformed of a one-turned loop, having no terminals derived therefrom,these are energized by wireless process. For this purpose, a primarycoil is provided: by connecting across the primary coil an alternatingcurrent source having a frequency resonant with that of the internalmovable plate to energize the internal movable plate. Thus the opticalaxis of the optical element 312 is allowed to swing in the manner oftwo-dimensional basis i.e., in two orthogonal directions.

As described above, since both the driving coils are formed of aone-turned loop and no wiring is needed, the construction thereof islargely simplified compared with the Related Art 2 or the like. Inaddition, since all that including driving coils and the mirror areformed by aluminum deposition and etching, the necessary number of masksis halved and the process is largely simplified to lead to improvedyield and lowered cost.

Also, due to the aluminum deposited layer for the driving coils, thestable characteristics and long life are expected.

MODIFIED FORMS

In a structure having a single movable plate as the Related art 1,instead of other arts having two movable plates, the construction isalso simplified.

Embodiment 3

Shown in a summarized view of the embodiment of FIG. 9, the embodimentis an example in which stoppers 612 and 613 for external movable platesas well as a stopper 614 for the internal movable plate are provided,for preventing damage of torsion bars caused by external shocks.

Other than provided with stoppers, the arrangement of permanent magnetsis also different fromt hat of the Related Art 2. Yet, there is noparticular difference in function as the electromagnetic actuator.Rather, according to the arrangement, utilizing the component ofmagnetic flux parallel to the driving coil, the number of permanentmagnets is reduced, the construction is simplified, and the low cost canbe realized.

FIG. 9 shows a summary view of an embodiment of an electromagneticactuator, in which the optical element 615 is caused to oscillate in thetwo-dimensional manner, similar to the actuator 610 in Related art 2,

The principal structure and function are substantially the same as thoseof Related art 2. Therefore, hereinafter described is the stopper.

In such an actuator, the torsion bar for swingably supporting themovable plate is constructed as shown in FIG. 11, including (a) asectional view, (b) a plan view and (c) a perspective view. As will befound in FIG. 11, the torsion bar Δy is strong in the lateral direction,but weak in the vertical direction.

The reason may be discussed in connection with a cantilever shown inFIG. 12. When a force F is applied to the end of a cantilever, thedisplacement Δy is represented by:

Δy=4×1³/(Gbt ³)×F

Also, when a force F′ is applied to the end of the cantilever, thedisplacement Δy′ is

Δy′=4×1³/(Gtb ³)×F

Suppose that b=3t, and F=F′:

Δy=4×1³/(G.3t.t ³)×F=1/3(4.1³ /G.t ⁴)×F

Δy′=4×1³/(G.t.27t ³)×F=1/27(4.1³ /G.t ⁴)×F

Where G is the lateral elastic coefficient. As a result:

Δy′=1/9.Δy

The displacement in the lateral direction is less than that in thevertical direction, and this shows the cantilever is stronger in theformer direction than the other.

Since a torsion bar made by the Si wafer is shaped as shown in FIG. 13,it is supposed to be weaker by a lateral shock than by a vertical shock,and it is found to be preferable to prevent an excessive displacementcaused by the vertical shock.

As the first method therefor, a stopper may be provided below themovable plate to reduce the probability of damage of the torsion bar.

Another method is to reduce the mass of the movable plate to decreasethe F, even if the equal amount of acceleration is exerted thereon,according to: F=ma

This second method is effective not only for the lateral but verticaldirections. By applying two methods at the same time, further increaseof anti-shock and anti-vibration is expected.

Utilizing the first method, FIGS. 14 and 15 shows the production processof embodiment 3. For ease of comprehension, the thickness direction isexaggerated in these figures, also the same in FIGS. 16 to 22.

FIGS. 14(a) to (g) show plan views on the right side, and each sectionalview taken along lines A-A′ viewed from the arrow direction. In each ofsteps: (a) an oxide layer 601 is formed on both faces of Si substrate600, (b) part of oxide layer 601 is removed by photolithography andoxide layer etching, (c) the Si surface from which the oxide layer 601has been removed is further etched. (d) oxidizing the etched Si surfaceto form a thin oxide layer 603; (e) selectively removing the oxide layer603 by photolithography and oxide layer etching, so as to leave theregions of stoppers 612 and 613 for the external movable plates and ofthe stopper 614 for the internal movable plate; (f) bonding a Pyrexglass plate 604 onto the surface of Si substrate 600, on which nostoppers 612, 613 and 614 are formed, by anode bonding method; (g)anisotropically etching the Si substrate 600, so as to leave the regionsof tip support 605, and stoppers 612, 613 and 614; and (h) removing theoxide layer 603 of tip support 605, and stoppers 612, 613 and 614 toobtain a support member 700 by etching.

Further, the steps include (i) bonding the chip 611 including theseparately fabricated movable plate, torsion bar and driving coil, etc.onto the support 700 formed as above-mentioned; and (j) mountingpermanent magnets 616 to complete the electromagnetic actuator. Morespecifically, as shown by FIG. 10, by arranging the chip 611 andpermanent magnets 616 in a package as the yoke 622 in position asillustrated, completing a necessary connection by the wire 624, thus theactuator 610 is completed.

“Anode plating” is a technology in which each flat surface of a siliconsubstrate and glass substrate are attached together, heated at 400° C.,and applied with a negative voltage of 100 V to complete bonding. Theionic deviation which occurs herein causes a static electrical forcebetween the silicon and glass substrates, which are bonded together dueto chemical binding produced on the interface.

As shown in FIG. 9 and step (j) in FIG. 15, the actuator is providedwith a plurality of, such as three, beam-like shaped stoppers opposed toone side of movable plates and outside of the range in which the movableplates are swingable. By provision of such stoppers 612, 613 and 614, anexcessive deformation of movable plates and damage of torsion bars areproperly prevented, even in the event that the movable plates receive anexternal shock or are driven in excess due to unknown causes. The methodis called “Second method”.

Embodiment 4

FIGS. 16 and 17 show the process sequence of the embodiment 4 similar toembodiment 3 and Related art 2, but is another example in which the“Second method” above is applied, thereby also to reduce the mass ofmovable plates and to prevent damage of torsion bars.

More specifically, when using a silicon wafer having a thickness of 200microns with the movable plate etched to the thickness of 50 microns,then the mass of the movable plate reduces to ¼ compared with theconventional. With the acceleration a caused by an external shock, andthe mass m is replaced by ¼.m, therefore the force F is:

F=¼.m α

Hence, the force F applied on the movable plate reduces to ¼, theprobability of damage of the torsion bar is largely reduced.

The silicon wafer having a thickness of 200 microns is used herein, andthe region of movable plates is etched to reach the -thickness of 100microns. The process sequence includes the steps of:

(a) forming oxide layers 801 and 802 on upper and lower faces of Sisubstrate 800 of 200 microns in thickness by oxidation;

(b) removing part of oxide layer 802 by photolithography and oxide layeretching;

(c) forming a thin oxide layer 803 by oxidation;

(d) selectively removing the oxide layer 803 by photolithography andoxide layer etching, so as to leave the regions including the firsttorsion bar 804, external movable plate 805, second torsion bar 806 andinternal torsion bar 807;

(e) further anisotropically etching the portion already oxide-layeretched in step (d);

(f) removing the still remaining oxide layer 803 by oxide layer etching;

(g) anisotropically etching the Si substrate 800 to form a first torsionbar 808, external movable plate 809, second torsion bar 810 and internalmovable plate 811;

(h) forming aluminum layer 901 on oxide layer 801 by aluminumdeposition;

(i) partially removing aluminum layer 901 by photolithography andaluminum etching to simultaneously form a first driving coil 902 or theexternal movable plate 809 periphery, a second driving coil 903 on theinternal movable plate periphery, and a mirror 904 as an opticalelement;

(j) selectively forming an organic protective layer 905 byphotolithography so as to cover the periphery, and the first, seconddriving coils 902 and 903; and

(k) removing the unnecessary oxide layer 802 by oxide layer etching tocomplete a chip 900 forming the main part of an electromagneticactuator. Thereafter, the chip 900 is interposed between the upper andlower glass substrates, a permanent magnet is mounted, and thus theelectromagnetic actuator is assembled.

As described, the movable plates are of thin films formed from the Sisubstrate to reduce their mass and the stress applied when receiving ashock. As a result, an excessive deformation of movable plates anddamage of torsion bars are prevented.

Embodiment 5

FIGS. 18 and 19 show the process sequence of the embodiment 5 featuredin combining provision of stoppers and reduction of the mass of movableplates, including the steps of:

(a) forming oxide layers 501 and 502 on upper and lower faces of Sisubstrate 500 of 200 microns in thickness by oxidation;

(b) selectively removing the oxide layer 502 by photolithography andoxide layer etching, so as to leave the regions including stoppers 504and 505 and peripheral region 506;

(c) forming a thin oxide layer 507 by oxidation;

(d) selectively removing the oxide layer 503 by photolithography andoxide layer etching, so as to leave the regions including the periphery506, the first torsion bar 508, external movable plate 509, secondtorsion bar 510 and internal movable plate 511;

(e) further anisotropically etching the portion from which the oxidelayer 507 has been removed in step (d);

(f) removing the still remaining oxide layer 507 by oxide layer etching;and

(g) anisotropically etching the Si substrate 500 to form a first torsionbar 512, external movable plate 513, internal movable plate 514 andsecond torsion bar 515.

Further steps include:

(h) forming aluminum layer 516 on oxide layer 501 by aluminumdeposition;

(i) partially removing aluminum layer 516 by photolithography andaluminum etching to simultaneously form a first driving coil 517 onexternal movable plate periphery, a second driving coil 518 on internalmovable plate periphery, and a mirror 519 as an optical element;

(j) selectively forming an organic protective layer 519 byphotolithography so as to cover the periphery, and the first, seconddriving coils 517 and 518; and

(k) removing the unnecessary oxide layer 502 by oxide layer etching tocomplete a chip 520 forming the main part of an electromagneticactuator; and thereafter,

(l) the chip 520 is placed and bonded on the chip support member 550formed in the same manner as embodiment 3, a permanent magnet isdiagonally mounted, and thus the electromagnetic actuator is completed.

As described above, provision of stoppers and weight reduction ofmovable plates provide prevention of damage of the torsion caused by theexternal shock.

Embodiment 6

The embodiment 6 shown in FIGS. 20, 21 and 22 is the process sequenceimproved with further highly utility in providing one or more stoppersand reducing the weight of movable plates:

In FIGS. 20, 21 and 22, the process sequence includes the step of:

(a) forming oxide layer 401, 402 on upper and lower faces of Sisubstrate 400 of 200 microns in thickness by oxidation;

(b) selectively removing the oxide layer 402 by photolithography andoxide layer etching, so as to leave the peripheral region 403;

(c) forming a thin oxide layer 404 by oxidation;

(d) selectively removing the oxide layer 402 by photolithography andoxide layer etching, so as to leave the regions including the firsttorsion bar 405, external movable plate 406, second torsion bar 407 andinternal movable plate 408;

(e) further anisotropically etching the portion from which the oxidelayer 407 has been removed in step (d);

(f) removing the still remaining oxide layer 404 by oxide layer etching;and

(g) anisotropically etching the Si substrate 400 to form a first torsionbar 409, external movable plate 410, second torsion bar 411 and internalmovable plate 412.

Further steps include:

(h) forming an aluminum layer 413 on oxide layer 401 by aluminumdeposition;

(i) partially removing aluminum layer 409 by photolithography andaluminum etching to simultaneously form a first driving coil 414 onexternal movable plate periphery, a second driving coil 415 on internalmovable plate periphery, and a mirror 416 as an optical element centeredin the internal movable plate;

(j) selectively forming an organic protective layer 418 byphotolithography over the first, second driving coils 414, 415 and theperiphery 417; and

(k) removing the still remaining portions 411 and 412 of oxide layer byoxide layer etching to complete a chip 419.

Further steps include:

(l) oxidizing the upper and lower faces of Si substrate 420 to formoxide layers 421 and 422;

(m) selectively removing the oxide layer 420 and 421 by photolithographyand oxide layer etching, so as to leave the regions of stoppers 423 and425 for the external movable plates and of the stopper 424 for theinternal movable plate;

(n) bonding a Pyrex glass plate 426 on lower face of Si substrate 420 byanode bonding method;

(o) further anisotropically, selectively etching Si substrate, leavingthe regions including stoppers 423, 424 and 425 to complete a chipsupport member 427; and

(p) bonding the chip 419 and chip support member 427 also by anodebonding method. Thereafter, in the same manner as embodiment 3,permanent magnets are mounted diagonally relative to chip 419, and thusthe electromagnetic actuator is completed.

With a simplified structure, the embodiment is practical and exhibitsthe same effect as embodiment 5.

Other than the two-dimensional motion, another type allows the opticalaxis of the optical element to oscillate one-dimensional, e.g., aboutone axis.

Instead of a mirror, a light-receiving or emitting element may be alsoemployed as the optical element.

The stopper may be arranged, not limited on one side of the movableplate, on both sides thereof.

Embodiment 7

In an actuator 1100 shown in FIG. 23 in summary, the optical axis of anoptical element 1108 is allowed to oscillate in two-dimensional manner,a first and a second driving coils 1105 and 1106 each is formed as aclosed circuit, and a primary coil 1107 is newly provided so as tocouple with the first and second coils 1105 and 1106 above: a current iscaused to flow, through the primary coil 1107, and indirectly in thefirst and second coils 1105 and 1106. Further included are respectiveexternal and internal movable plates 1109, 1110, and, first and secondtorsion bars 1111 and 1112, respectively.

The wiring patterns for torsion bars 1111 and 1112 are unnecessary andomitted, and also different from the Related art 2 in the arrangement ofmagnets 1103 and 1104 , and the method of driving. But there is nodifference in function in spite of the different arrangement of magnets1103 and 1104, rather providing a simplified construction.

FIGS. 24 to 26 include plan views on the right side and sectional viewstaken along each of lines A—A on the left side.

In FIGS. 24, 25 and 26, the process sequence of the chip 1101 includesthe steps of:

(a) forming oxide layer 1201, 1202 on upper and lower faces of Sisubstrate 1200 by oxidation;

(b) selectively removing the oxide layer 1202 by photolithography andoxide layer etching, so as to leave the regions including peripheralregion 1203, external movable plate 1204 and internal movable plate1205;

(c) oxidizing the region already removed in step (d) to form a thinoxide layer 1206;

(d) selectively removing the oxide layer 1202 by photolithography andoxide layer etching, so as to leave the regions including the firsttorsion bar 1207, external movable plate 1204, second torsion bar 1208and internal movable plate 1205;

(e) anisotropically etching the portion from which the oxide layer hasbeen removed in step (d);

(f) removing the still remaining oxide layer 1206 by oxide layeretching; and

(g) further anisotropically etching from the lower face of siliconsubstrate 1200.

Referring now to FIG. 25, further steps include:

(h) forming aluminum layer 1209 on oxide layer 1201 by aluminumdeposition;

(i) partially removing aluminum layer 1209 by photolithography andaluminum etching to simultaneously form a single-turn closed loopedfirst driving coil 1105, an also single-turn closed looped seconddriving coil 1106, and a mirror 1108 as an optical element;

(j) selectively forming an organic protective layer 1210 byphotolithography so as to surround the periphery 1203, and the first,second driving coils 1105, 1106; and

(k) removing the unnecessary portions 1211 and 1212 of oxide layer 1201by oxide layer etching to complete a chip 1100.

FIG. 26 shows the process sequence of support assembly 1102 includingthe steps of:

(a) forming aluminum layer 1301 on a Pyrex glass base 1300 by aluminumdeposition;

(b) selectively removing aluminum layer 1301 by photolithography andaluminum etching to form the first turn 1302 of primary coil 1107 andone terminal 1303 therefor;

(c) forming an insulating layer 1304 entirely on the upper face of thebase;

(d) forming an aluminum deposited layer 1305 over insulating layer 1304;

(e) selectively removing aluminum layer 1305 by photolithography andaluminum etching to form the second turn 1306 of primary coil 1107 andthe other terminal 1307 therefor;

(f) forming an organic protective layer 1308 on the upper face entirely;and

(g) bonding a spacer 1309 around the periphery to complete the supportassembly 1102.

ASSEMBLY: FIG. 27 shows the sequence of assembly comprising the stepsof:

(a) bonding the chip 1101 shown in step (k) of FIG. 25 on the supportmember 1102 in step (g) of FIG. 26; and

(b) mounting the magnets 1103, 1104 on the opposite sides relative tochip 1101 to complete the actuator 1100. The S-pole of magnet 1103 andthe N-pole of magnet 1104 are connected through a yoke, which servesalso as a package, but not shown.

ACTUATION: The manner of actuating the actuator is described referringto FIG. 28 wherein both the external and internal movable plates 1109and 1110 (FIG. 23) are allowed to oscillate in the resonant state, andassume the resonant frequencies for external and internal plates are 375and 1500 Hz, respectively.

As shown in FIG. 28(a), first, a first sine wave a.c. source 61 and asecond sine wave a.c. source 62 are connected in series, and connectedto the primary coil 1107 in order to actuate the device. Then, throughthe first and second driving coils 1105 and 1107, which areelectromagnetically coupled to primary coil 1106, each of the currentsof 375 and 1500 Hz flows in each of the coils 1105 and 1106,respectively. As a result, the external and internal movable plates areactuated in resonant state of 375 and 1500 Hz, respectively, and theoptical axis of optical element 1108 is allowed to oscillate as one ofLissajous FIG. 63 as shown by FIG. 28(b).

The amplitude χ in the x-direction can be varied by variation of voltagee of the a.c. source 61, and, similarly, the amplitude γ in they-direction by variation of voltage e₂ of the a.c. source 62. When theratio of resonant frequencies between the external and internal movableplates 1109 and 1110 is selected so as not to coincide with any integer,the Lissajous figure moves and a fine scanning becomes possible.

Instead of actuating using a power source having a small internalimpedance, also a source having a larger internal impedance may be used,by connecting both sources in parallel to terminals 1303 and 1307. Inaddition, as the resonant characteristic of an electromagnetic actuatorof the type is extremely steep (i.e. having a high mechanical Q), theexternal movable plate 1109 would not be actuated by the current of 1500Hz, and the internal movable plate 1100 would not be actuated by thecurrent of 375 Hz.

As discussed above, according to the invention, no provision of wiringpatterns on the torsion bars enables a long life, and the simplifiedproduction process provides the improved yield and low cost inproduction.

Embodiment 8

FIG. 30 shows an electromagnetic actuator, in which a chip 81 asdescribed above is vacuum sealed by a Pyrex glass base 82 and 85 andsilicon spacers 83 and 84, by which seal the response characteristics isimproved and time degradation is prevented.

The primary coil 86 is formed out of sealed region or on the externalarea of the electromagnetic actuator. 83 84 81

Bonding of Si spacers 83, 84 with chip 81 is performed by anode bondingwith forming a Pyrex glass layer by sputtering on the side of spacer.Bonding of Pyrex glass 82 with Si spacer 83, 84, and also bonding ofPyrex glass 85 with Si spacers 84, are also by anode bonding. This anodebonding includes: close aligning each smooth surfaces of Si and glassbases, heating up to 400° C., and applying a negative voltage of severalhundred volts on the side of the glass to achieve bonding.

The embodiment is actuated in the same manner as the foregoingembodiment 7.

Although formed of vacuum sealed type, there is no leadout wiring out ofthe primary and secondary driving coils, and, therefore, the sealreliability is sufficiently high. The same effect can be attained by agas seal which is of the type for sealing against an inactive gas,instead of vacuum seal.

Embodiment 9

FIG. 31(a) shows the principal construction of the embodiment 9 andmethod of actuation therefor, in which a carrier frequency is used foractuation from the primary coil to the first driving coil or to thesecond driving coil.

In either of embodiments 7 and 8, the primary coil, first driving coiland the second driving coil together form a coreless transformer.Therefore, as leakage flux is increased, the actuating frequency is lowand energy transfer efficiency is also low.

The matter of leakage flux can be solved to a some extent by decreasingthe distance between the primary coil and first and second driving coilsas small as possible. The matter of biasing frequency is, in the case ofthe embodiment 9, solved by utilizing a carrier of several hundred KHz.

As shown in FIG. 31(a), the first driving coil 95 forms a closed circuitthrough a diode 97, and the second driving coil 96 forms also a closedcircuit through a diode 98. As a result, each of these closed circuitsforms a mean value type diode detection circuit. Diodes 97 and 98 areformed by a known semiconductor technology on the external and internalmovable plates, respectively. Hereinafter it is discussed, when theresonant frequency of the external movable plate is assumed to 375 Hz,while that of the internal movable plate 1500 Hz, and carrier frequency400 KHz.

A sine wave a.c. source 91 of 375 Hz and another sine wave a.c. source92 of 1500 Hz are connected in series to provide a composite wave,applied to an amplitude modulation circuit 93, and a separatelygenerated carrier of 400 KHz is modulated.

Using thus formed amplitude modulated frequency, the primary coil 94 isactuated. As a result, based on the electromagnetic coupling with theprimary coil 94, a modulated frequency is in induced in each of thefirst and second driving coils, each being demodulated by each ofdiodes.

Currents of 375 Hz, 1500 Hz as well as the d.c. component each flow inboth the first and second coils. Therefore, the first driving coil 95 isactuated in resonant state by the current of 365 Hz, while the seconddriving coil 96 is actuated in resonant state by the current of 1500 Hz.

As a result, the optical axis of the optical element such as a mirror iscaused to oscillate so as to trace a Lissajous figure 99 in FIG. 31(b).

The amplitude χ in the x-direction can be varied by variation of voltagee of the a.c. source 91, and, similarly, the amplitude γ in they-direction by variation of voltage e₂ Since the external and internalmovable plates are actuated into the resonant state, the extent of beingdriven by the current of d.c. component is merely negligibly few.

The energy transfer efficiency between the first and second coils can beincreased. In addition, when the ratio of resonant frequencies betweenthe internal and external sides is selected so as not to be any integer,a scan of even a rectilinear figure is realized.

The invention can be applied also for an electromagnetic actuator havingonly one movable plate, other than having two or more plates aspreviously discussed.

Alternatively, another feature is possible, so that the first drivingcoil is supplied with a current via terminals, while only the seconddriving coil is actuated by means of inductive coupling by the primarycoil. In such a case, the current induced in the first coil due toactuation by the primary coil can be blocked by in series connecting, asnecessary, a choke coil between the first coil and its power source,where the external movable plate is permitted to be driven in a stateother than the resonance, e.g. by a sine waveform or sawtooth waveformof an arbitrary frequency.

Also, not limited as having a single turn, any one of driving coils maybe of a plurality of turns.

As to materials, not limited as formed of aluminum, any of others, suchas copper or gold layer, may be employed.

Accordingly, the invention provides an electromagnetic actuator with alow cost, a stabilized life, and improved strength against physicalshocks.

At least part of the wiring for torsion bars can be also saved, and thisis to in turn contribute the long life of use.

Industrial Utility

The invention is widely applicable for optical scanners or sensors for avariety of information equipment, such as bar code scanners, CD-ROMdrives, or sensors for automatic booking machines.

What is claimed is:
 1. An electromagnetic actuator comprising: anexternal movable plate formed integrally with a semiconductor substrate;a first torsion bar for movably supporting said movable plate withrespect to said semiconductor substrate; an internal movable platedisposed inside said external movable plate; a second torsion barrotatably supporting said internal movable plate relative to saidexternal movable plate, and positioned at a right angle relative to saidfirst torsion bar; further including: a single turn first driving coilextending around said external movable plate; a single turn seconddriving coil extending around said internal movable plate, and connectedin series to said first driving coil; magnetic field generating meansfor applying a magnetic field to said first and second driving coils;and an optical element having an optical axis and located on saidinternal movable plate; wherein a current is caused to flow through saidfirst and second driving coils to produce a force corresponding to eachcoil and to each plate, said external and internal movable platesdisplacing in response to the corresponding coil forces applied theretoand thus vary the direction of displacement of said optical axis.
 2. Theelectromagnetic actuator of claim 1 wherein the single turn first andsecond driving coils are closed-looped.
 3. A method of manufacturing theelectromagnetic actuator according to any one of claims 1 or 2comprising: forming an aluminum layer on the semiconductor substrate byaluminum deposition; and forming said driving coils from said aluminumlayer through photolithography and aluminum etching.
 4. A method ofmanufacturing the electromagnetic actuator of claim 3 comprising formingsaid optical element as a mirror at the same time as the forming of saiddriving coils from said aluminum layer through photolithography andaluminum etching.
 5. A method of manufacturing the electromagneticactuator of claim 3 comprising forming wiring on said torsion bar forcoupling said driving coils at the same time as the forming of saiddriving coils from said aluminum layer through photolithography andaluminum etching.
 6. The electromagnetic actuator of claim 1 whereinsaid external and internal movable plates are each formed as a thin filmfrom said semiconductor substrate, said thin film being thinner thansaid semiconductor substrate and substantially no thicker than saidtorsion bar.
 7. An electromagnetic actuator comprising: a pair ofmovable plates formed integrally with a semiconductor substrate; atleast one torsion bar for movably supporting said movable plates withrespect to said semiconductor substrate; a driving coil extending aroundeach said movable plates; magnetic field generating means for applying amagnetic field to each of the driving coils; an optical element formedon one of said movable plates and having an optical axis; and a primarycoil electromagnetically connected to each of said driving coils;wherein a current caused to flow through said primary coil and in eachsaid driving coil creates a force corresponding to each driving coil andto each plate, each said movable plates displacing in response to theapplied corresponding force to thereby vary the direction ofdisplacement of said optical axis.
 8. The electromagnetic actuator ofclaim 7 wherein: one of the pair of plates is an external movable plateand the other of the pair of plates is an internal movable platedisposed inside said external movable plate; the torsion bar comprises afirst torsion bar for movably supporting said external movable platewith respect to said semiconductor substrate and a second torsion barmovably supporting said internal movable plate relative to said externalmovable plate, and positioned at a right angle relative to said firsttorsion bar; the driving coils comprising a first driving coil formed asa closed-loop extending around said external movable plate and a seconddriving coil formed as a closed-loop around said internal movable plate;the magnetic field generating means for applying a magnetic field tosaid first and second driving coils; the optical element being formed onsaid internal movable plate.
 9. The electromagnetic actuator of claim 7wherein the driving coil about each plate forms a closed loop andincludes a diode; and further includes means for flowing a modulationcurrent in said primary coil so that a demodulation current flowsthrough said driving coil in response to said modulation current in saidprimary coil to create said force associated with each driving coil andassociated with each plate to vary the direction of the displacement ofsaid optical axis.
 10. The electromagnetic actuator of claim 9 wherein:the movable plates include an external movable plate and an internalmovable plate disposed inside said external movable plate; the torsionbar comprises a first torsion bar for movably supporting said externalmovable plate with respect to said semiconductor substrate and a secondtorsion bar movably supporting said internal movable plate relative tosaid external movable plate, and positioned at a right angle relative tosaid first torsion bar; the optical element being formed on saidinternal movable plate.
 11. The electromagnetic actuator of any one ofclaims 8 to 10 wherein the area including the movable plates, torsionbar and second driving coil is arranged in a vacuum or gas encapsulatedregion and said first driving coil is disposed outside said region. 12.The electromagnetic actuator of claim 8 wherein the primary coil anddriving coils are arranged so that current flows in said first andsecond coils in response to a current in said primary coil.
 13. Theelectromagnetic actuator of claim 8 including means for applying acurrent to the first driving coil, the primary coil for applying amodulated current to said second driving coil, the second driving coilincluding means such that a demodulated current flows in said seconddriving coil, said currents for creating said corresponding force.
 14. Amethod of manufacturing the electromagnetic actuator of any one ofclaims 7 to 10 and 12-13 comprising depositing an aluminum layer on saidsemiconductor substrate by vacuum evaporation, and forming said drivingcoils from said aluminum layer through photolithography and aluminumetching.
 15. The method of manufacturing the electromagnetic actuator ofclaim 14 comprising depositing an aluminum layer on said semiconductorsubstrate by vacuum evaporation, and forming the optical element anddriving coils simultaneously from said aluminum layer by saidphotolithography and etching, the optical element comprising a mirror.